Malignant gliomas are the most common primary brain tumors. The long-term objective of this proposal is to establish a mouse model of malignant gliomas, which recapitulate the essential features of the tumor. Gliomagenesis is a multi-step process, which likely involves the amplification of oncogenes and inactivation of tumor suppressors. The INK4a tumor suppressor locus has been implicated in gliomagenesis. INK4a null astrocytes are immortal in cultures but unable to form glioma in vivo. Identification of tumor suppressor and/or oncogenes, which cooperate with the null mutation of INK4a locus in gliomagenesis is proposed. An expression selection of genetic suppressor elements (GSEs) derived from INK4a null astrocytes will be employed to identify tumor suppressor genes cooperating with the INK4a deficiency in gliomagenesis. This library would contain suppressors of practically all cellular genes such as tumor suppressors. To isolate the amplified oncogenes in gliomas, full-length cDNA library of a glioblastoma cell line will be introduced into INK4a null astrocytes. Alternatively, retroviral insertion mutagenesis will be performed to identify the amplified oncogenes in gliomas. Roles of the putative tumor suppressors and oncogene candidates in cell growth, apoptosis, and cell cycle regulation will be evaluated. Knock-out and transgenic mice of one putative tumor suppressor and one oncogene candidate will be generated and crossed with the INK4a null mice to understand the relationship between these new genes and INK4a in gliomagenesis. The resultant compound mice will be examined for the formation of gliomas.